The main rocket engine for the existing Space Shuttle vehicle (SSME) includes in its fuel systems in certain versions a gaseous oxygen heat exchanger in the liquid oxygen turbopump turbine exit flow path. The purpose of this heat exchanger is to heat a portion of the liquid oxygen to its gaseous state so that it can be utilized to pressurize the oxygen tank and the POGO (a stabilizing system in the SSME liquid oxygen inlet line). The energy to heat the oxygen is taken from preburner combustion gas as this hot gas exists from the turbine of the liquid oxygen turbopump. The hot gas is routed to surround the coils of the heat exchanger that is mounted in the LOX turbopump turbine housing. The hot gas which is extremely hydrogen rich, surrounds these heat exchanger coils and is at a much higher pressure than the pressure of the oxygen within the coils. Obviously, if a rupture of the coils should occur the higher pressure hot hydrogen will enter the heat exchanger and flow to the oxygen tank which could ultimately result in the explosion of this tank.
While heat exchangers are typically used in the liquid rocket fuel systems, these heat exchanger are either used to increase the temperature of the oxidizer and/or fuel before being admitted to the combustion chamber's fuel injector or utilized in a regenerative system so as to raise the fuel temperature at the low pressure turbine inlet in order to pump the propellant for engine output power. Examples of such systems are disclosed in U.S. Pat. Nos. 4,589,253 granted to Wagner on May 20, 1986 entitled "Pre-Regenerated Staged-Combustion Rocket Engine", 4,583,362 granted to Wagner on Apr. 22, 1986 entitled "Expander-Cycle, Turbine-Drive, Regenerative Rocket Engine", 5,101,622 granted to Bond on Apr. 7, 1992 entitled "Aerospace Propulsion", 3,049,870 granted to Chamberlain on Aug. 21, 1962 entitled "Rocket Propellant Cycle", 2,930,187 granted to Chillson et al on Mar. 29, 1960 entitled "Variable Thrust Rocket Engine" and 4,771,599 granted to Brown et al on Sep. 20, 1988 entitled "Tripopellant Rocket Engine with Injector", the latter patent being assigned to United Technologies Corporation the assignee common to this patent application.
We have found that we can obtain an efficacious system for a rocket engine for pressurizing the oxygen tank without having to change or modify the existing internal heat exchanger of the SSME by converting the heretofore known gaseous oxygen heat exchanger (GOX/HEX) to a hydrogen heat exchanger (H.sub.2 /HEX). The source of hydrogen for the converted internal H.sub.2 /HEX is selected such that the pressure of the hydrogen is higher than the pressure of the hot gas surrounding the heat exchanger coils. Accordingly, the hydrogen would leak out from a fractured coil rather than hot hydrogen-rich gas leaking into the coil.
According to this invention an external heat exchanger is added to indirectly transfer heat from the hot hydrogen to the liquid oxygen to create a gas. This external heat exchanger is a self-contained unit that can easily be added to the existing SSME system. Only minor modifications are necessary to the fluid ducting of the current engine in order to convert the existing internal heat exchanger from oxygen to hydrogen. Of importance is that no control systems are necessary to adapt this invention to the current SSME. All flows are controlled with existing valves and trimmed out using pressure balances and flow restrictions as will be described hereinbelow.